Post on 15-Apr-2017
Liquid CrystalsLiquid CrystalsChapter 8, Box 8.1Chapter 8, Box 8.1
MesophaseMesophase
Solid Mesophase Liquid
Common Shapes: Common Shapes: AnisotropicAnisotropic
Thin, Long Disk-shaped
Liquid CrystalLiquid Crystal TransitionTransition
– Temperature (Temperature (thermotropicthermotropic))– Pressure (Pressure (lyotropiclyotropic))
Mesophase, Liquid Crystal
Solid Liquid
Types of long range Types of long range orderorder
Nematic phaseNematic phase– Parallel alignmentParallel alignment– Lack layer Lack layer
arrangementarrangement
Smectic phaseSmectic phase– Parallel alignmentParallel alignment– LayeredLayered
Cholesteric phaseCholesteric phase– Molecules lie in sheets Molecules lie in sheets
at different angles at different angles (helical structure). (helical structure).
Importance of Cholesteric Importance of Cholesteric phasephase
– Form Helical Form Helical structurestructure(dependent on (dependent on temp.)temp.)
Diffract lightDiffract light Colors Colors
LCD LayersLCD Layers
Twisted nematic LCDTwisted nematic LCD
•Twisted: rotates polarized light 90o
•Supertwisted: rotates polarized light 270o
Nematic Crystals•Anisotropic optical properties•Response to electric fields•Used in Liquid Crystal Display
Optical ResponseOptical Response
•Applied voltage changes tilt angle of nematic layers•Tilt Angle changes light transmission
Super-Twisted Nematic Super-Twisted Nematic LCDLCD
270o 90o
•Abrupt tilt angle change with 270o twist•On/Off response faster•210o used for grayscale
Obtaining a Useful Obtaining a Useful Temperature RangeTemperature Range
•Nematic exists over larger range than either separate solution does
ConclusionsConclusions Mesophase valuable toolMesophase valuable tool LCD one example of applicationLCD one example of application
ReferencesReferences1.1. Atkins, P. and Julio de Paula. Atkins, P. and Julio de Paula. Physical ChemistryPhysical Chemistry. 7. 7thth ed. ed.
W.H. Freeman and Co. New York: 2002; 209-210.W.H. Freeman and Co. New York: 2002; 209-210.2.2. ““Chemical of the Week: Liquid Crystals.” University of Chemical of the Week: Liquid Crystals.” University of
Wisconsin-Madison. Wisconsin-Madison. http://scifun.chem.wisc.edu/chemweek/LiqXtal/LiqXtal.htmhttp://scifun.chem.wisc.edu/chemweek/LiqXtal/LiqXtal.htmll
3.3. ““Introduction to Liquid Crystal Displays.” Introduction to Liquid Crystal Displays.” http://plc.cwru.edu/tutorial/enhanced/files/lcd/tn/tn.htmhttp://plc.cwru.edu/tutorial/enhanced/files/lcd/tn/tn.htm